As represented by a base station in a mobile communication system, there is a wireless communication device that performs wireless communication with a plurality of remote stations. The wireless communication device amplifies a transmission signal by a power amplifier and transmits the signal. Conventionally, there has been known a signal processing technique referred to as peak suppression that enables to use the power amplifier near a saturated region having high power efficiency (for example, see Japanese Laid-open Patent Publication No. 2007-251909).
In the peak suppression, generally, a hard clipping process is performed to perform amplitude limiting on the transmission signal with a predetermined threshold, and out-of-band radiation power generated due to the hard clipping process is removed by a filter.
If a peak suppressing signal is extracted by subtracting the original transmission signal from the peak-suppressed transmission signal to analyze frequency components of the peak-suppressed signal, there is a tendency such that the peak suppressing signal appears in a larger value in a frequency exhibited in a central portion of a frequency band of the transmission signal, as compared to a frequency exhibited in an end portion thereof.
Although a peak suppressing process is required for efficient use of the power amplifier, after all, it means that a noise component is added to the transmission signal. In a multicarrier transmission system in which the frequency band of the transmission signal is divided into a plurality of frequency domains to perform communication, the quality of transmission signals differ from one carrier to another due to peak suppression. Specifically, the quality of a transmission signal in the frequency domain at the central portion of the frequency band is deteriorated as compared to the quality of a transmission signal in the frequency domain at the end of the frequency band.
However, when an orthogonal frequency division multiplexing (OFDM) system is applied to a mobile communication system, peak suppression for using the power amplifier in the saturated region having high power efficiency is essential, and equalization of the quality of the transmission signals in their respective frequency domains when the suppressing process is performed on the transmission signal becomes a task.